The present invention is an improvement over the conveyor system described in U.S. Pat. No. 4,133,667, which patent is hereby incorporated herein by reference; therein, the glass manufacturing process generally takes place through a succession of related steps that are carried out at separate stations in an overall glass manufacturing system and each of the stations generally has correspondence to one of the manufacturing steps.
Glass material is conveyed through each of the successive stations at a controlled rate. The glass sheets are conveyed between and within a station by a conveyor mechanism defined by a pair of cooperative conveyor drives spaced apart from one another at opposite sides of the station. Each of the conveyor drives are defined by a continuous drive loop trained over a pair of cooperative pulleys. A plurality of elongated, cylindrical rollers are spaced apart from one another with respect to the direction of glass movement, and have their opposed ends supported on the respective conveyor drives in frictional engagement therewith. The cooperative rotation of the conveyor drives imparts rotational motion to the rollers. A glass sheet carried on the rollers is transported through a station in accordance with the net driving torque applied to the conveyor drives.
As described in U.S. Pat. No. 4,133,667, when the chain of a flat-top steel drive chain and sprocketed pulley arrangement is accelerated or decelerated through the range of zero to one-third of its normal operating speed, it vibrates. These vibrations are due to the slip-stick friction phenomenon that frequently occurs in mechanical drive systems.
Another characteristic of such a chain drive in an oscillating roller-hearth furnace that oscillates a glass sheet load within the furnace by alternately driving the chain sprocket forward and backward is an appreciable amount of lost motion caused by the slack present in the drive chain. This lost motion effect causes the rollers to be momentarily stopped even though the sprocket driving the chain is moving smoothly.
The mechanism described in U.S. Pat. No. 4,133,667 eliminates vibration and lost motion is most minimum tension, dual ended systems. This is accomplished by maintaining a minimum predetermined amount of tension in the active portion of the continuous drive loop by the application of a counter torque to the driven sprocket. However, in larger systems, more rollers are required and thus there are more friction points spaced closer together. In addition, larger motors, which have a slower response, are required.